The present invention is directed to a method and apparatus for converting long tube vertical evaporators to falling film evaporators.
Long tube vertical evaporators (LTV) have heretofore been widely used, particularly in the pulp and paper industry. Such evaporators typically include a heat exchange chamber disposed between a bottom chamber and a vapor separation chamber. The heat exchanger chamber has a plurality of heat exchange tubes positioned therein which vertically extend between an upper tube sheet and a lower tube sheet. The bottom chamber extends below the heat exchanger chamber in fluid communication with the lower ends of the heat exchange tubes. The vapor separation chamber extends around and above an upper portion of the heat exchanger chamber in fluid communication with the upper ends of the heat exchange tubes. Feed liquid to be treated enters the bottom chamber through a feed inlet associated therewith and is directed upwardly through the heat exchange tubes. A vapor, such as steam, is directed into the heat exchanger chamber through a vapor inlet associated therewith, which causes at least a portion of the liquid passing through the heat exchange tubes to vaporize as it passes upwardly therethrough. A mixture of vapor and liquid passing through the upper ends of the heat exchange tubes is directed into the vapor separation chamber, wherein the vapor is separated from the liquid and is removed through a vapor outlet associated with an upper portion thereof and the liquid is removed through a product outlet associated with a lower portion thereof.
Falling film evaporators have heretofore been widely used in systems wherein the feed liquid is heat sensitive or requires low residence time and wherein low temperature differences exist. These evaporators typically have high heat transfer coefficients. Such evaporators typically include a heat exchanger chamber disposed between an upper distribution chamber and a vapor separation chamber. The heat exchanger chamber is of similar design as the heat exchanger chamber as discussed hereinabove with regards to the long tube vertical evaporator. The distribution chamber is positioned above the heat exchanger chamber in fluid communication with the upper ends of the heat exchange tubes positioned in the heat exchanger chamber. The vapor separation chamber extends below the heat exchanger section in fluid communication with the lower ends of the heat exchange tubes. Feed liquid to be treated enters the upper distribution chamber through a feed inlet associated therewith and is directed downwardly through the heat exchange tubes in the form of a vertical falling film. A vapor, such as steam, is directed into the heat exchanger chamber through a vapor inlet associated therewith, which causes at least a portion of the liquid passing through the heat exchange tubes to vaporize as it passes downwardly therethrough. A mixture of vapor and liquid passing through the lower ends of the heat exchange tubes is directed into the vapor separation chamber, wherein the vapor is separated from the liquid and is removed through a vapor outlet associated with an upper portion thereof and the liquid is removed through a product outlet associated with a lower portion thereof.
It is the latest thought in many industries, particularly in the pulp and paper industry, to utilize the falling film evaporator design. It has heretofore been necessary to scrap existing long tube vertical evaporators and purchase new falling film evaporators in order to convert over to the falling film type of evaporator. The present invention is specifically directed to a method and apparatus which permits such a conversion while salvaging a large portion of the existing apparatus.